Re-Oaking

Before 1900, native oaks were abundant in many of California’s valleys. These trees thrived on hot open plains, enabling them to endure California’s long dry season and frequent drought. Oaks also played a foundational role for an exceptionally diverse array of native wildlife, reflecting a deep shared history of coexistence. By the early 1900s, agricultural conversion of many of California’s most fertile valleys had eliminated many oak woodlands. During the 20th century, urban expansion led a second transformation, replacing agriculture with cities as California’s economy boomed.

Today, the plants and animals that are distinctive of oak woodlands have vanished from our cities, replaced by vegetation from around the world and urban-adapted wildlife. These urban ecosystems do not provide the same support for wildlife, and they are not ideally suited to thrive through drought or hot summer temperatures. For example, trees from the eastern United States are adapted to frequent rainfall during the summer, and require irrigation to survive through California’s dry season.

“Re-Oaking” is an approach to reintegrating oaks and other native vegetation within the developed California landscape to restore this ecologically diverse and distinctive ecosystem to our cities. This idea could benefit people too - native oaks are drought- tolerant, provide heat-tempering shade in the summer, and sequester more carbon than many other common urban trees. Drawing on the beauty of California oak woodlands, Re-oaking could also help bring a unique sense of place back to our cities. As we design ecologically healthy and resilient cities of the future, Re-oaking could help integrate nature into our urban landscapes to benefit both ecosystems and people.

Re-Oaking Silicon Valley

In Silicon Valley, oak ecosystems were the defining feature of the landscape before large-scale transformation. Oak savannas and woodlands were so extensive that the valley was christened the Llano de los Robles, or Plain of the Oaks, by early explorers. In little more than a century, Silicon Valley’s oak woodlands were felled, replaced with orchards, and then replaced again with a patchwork of urban trees.

The rapid and continuing transformation of Silicon Valley creates an unusual opportunity to recover some of the region’s natural heritage by re-incorporating elements of oak woodland ecosystems. These changes could contribute to building landscape resilience in the region, increase biodiversity, and benefit people. Much of Silicon Valley's urban forest, planted 50-75 years ago, is nearing the end of its lifespan. Over the next few decades, local communities will create the next urban forest, shaping the sense of place, human health, and biodiversity of Silicon Valley for the rest of the 21st century. Given the challenges of drought and climate change, do Silicon Valley's native oaks – largely gone for a century – have a greater role to play in the coming century? This report begins to explore that question, focusing first on the benefits the re-oaking could have for local biodiversity and native wildlife.

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Drawing on resilience science, regional data, and local expertise, we will develop the vision and tools that will allow stakeholders in the region ensure that local actions contribute toward the creation of a high-functioning and resilient Silicon Valley ecosystem.

SFEI and Google have won the Arnold Soforenko Award from the non-profit Canopy for significant contributions to the urban forest. The award is for our work on Re-Oaking Silicon Valley: Building Vibrant Cities with Nature.

The award ceremony was held at Palo Alto City Hall on January 25, 2018.

Could restoring lost ecosystems to cities play a role in building ecological resilience across landscapes? In Re-oaking Silicon Valley, a new report by SFEI, we explore this opportunity in our region. Both beautiful and functional, native oaks can be excellent choices for streetscapes, backyards, and landscaping. Requiring little water after establishment, oaks can save money by reducing irrigation requirements while sequestering more carbon than most other urban trees common to our region.

Over the past century, oaks have been lost from fertile valleys across California to make way for agriculture, and then for cities. Yet cities could make room for their return; by harnessing the many greening activities that are already occurring, oaks could be planted along streets, in yards, and on corporate campuses. Re-oaking could help build ecological resilience while providing benefits for people such as carbon storage and water savings.

A collaborative program with the California Academy of Sciences produced an immersive tour from the canopy to the cosmos inside Morrison Planetarium, exploring the history and ecology of one of California’s most iconic and threatened tree species, the Valley oak. Academy scientists, indigenous partners, and historical ecologists from the San Francisco Estuary Institute revealed how Valley oaks and humans are intertwined in a relationship of disturbance and adaptation, with implications for the health and well-being of Bay Area communities.

The re-oaking concept developed by SFEI was featured in an article about Oakland and Silicon Valley. First conceived in a paper in Restoration Ecology by SFEI and UC Santa Barbara scientists, re-oaking is the strategic reintroduction of oaks and other native trees to California's urban, suburban, and agricultural valleys to recover lost functions and values.